The wavelength of an exposure light source used in the manufacture of semiconductors is becoming shorter as the pattern size shrinks. More specifically, the exposure light source has shifted from an i-line to an excimer laser, and its laser light source has also shifted from KrF to ArF. To establish a finer patterning technique, use of an F2 laser is under study.
To construct an exposure system using an F2 laser as the light source, the problem of attenuation of the exposure light energy must be solved. As the energy of an F2 laser beam is absorbed by the moisture or oxygen contained in the atmosphere, a conventional exposure apparatus cannot be applied as it is.
As a means for enabling adaptation to the F2 laser, a method of sealing a space where exposure light passes with a partition, or the like, and filling this space with an inert gas such as nitrogen may be possible. This system, however, also requires an inert gas temperature adjusting system and a circulating system for setting the temperature of the space in which a wafer and reticle are arranged at a constant temperature and for removing temperature fluctuation.
FIG. 3 is a schematic view of a conventional inert gas circulating system. A wafer space 21 and reticle space 22 in the exposure apparatus main body are surrounded by partitions 23 and the interiors of the partitions 23 serve as sealed spaces. A temperature adjusting gas blow-off portion 24 and exhaust portion 25 are connected to each space.
The temperature adjusting gas blow-off portions 24 are provided with filters 26, respectively. The temperature-adjusted clean inert gas flows are blown off into the wafer space 21 and reticle space 22. The inert gas flows blown off into the wafer space 21 and reticle space 22 absorb heat generated in the wafer space 21 and reticle space 22, and are exhausted through the exhaust portions 25. The inert gas flows are supplied to a cooler 29 through return ducts 28 and are heat-exchanged with a refrigerant 30. Then, the inert gas flows are heated and temperature-adjusted by heaters 31, supplied to the temperature adjusting gas blow-off portions 24, and circulated.
High-purity inert gas flows are supplied in predetermined amounts into the wafer space 21 and reticle space 22 through inert gas injection valves 27, and the gas flows in the wafer space 21 and reticle space 22 are exhausted in predetermined amounts through exhaust valves 35, so that the purities of the inert gas flows in the wafer space 21 and reticle space 22 are maintained.
The inert gas flows are temperature-adjusted in the following manner. Temperature sensors 32 detect the temperatures of the inert gas flows in the wafer space 21 and reticle space 22. Detection signals are supplied to temperature adjusting units 33, and outputs from the temperature adjusting units 33 are supplied to the heaters 31 by PID feedback control. Thus, the inert gas flows are controlled such that their temperatures become constant at portions where the temperature sensors 32 are set. The inert gas flows are circulated by a blower 34 arranged between the cooler 29 and heaters 31.
The conventional inert gas circulating system has the following problems in the case of periodical maintenance such as cleaning a wafer chuck arranged in the sealed space, or trouble such as a wafer lost.
(1) When the operator needs to access the sealed space, the interior of the sealed space is very dangerous as it is filled with the inert gas. Accordingly, an exclusive air purge blower or the like is required.
(2) When the interior of the sealed space is purged with air, the filter absorbs the moisture. Accordingly, when restoring the sealed space to a space filled with the inert gas, the moisture of the filter has a bad influence.
(3) When a gas containing moisture passes through the cooler, condensation occurs. The condensed water adversely influences circulation of the inert gas.
In particular, problems (2) and (3) largely influence the time necessary for purging with the inert gas at the start-up of the exposure apparatus, and may accordingly degrade the throughput remarkably.